Signaling system



July 19, 1938. F. CALHOUN SIGNALING SYSTEM Filed Feb. 17, 19s? 2 Sheets-Sheet 2 TIME TIME

FIG. 5

INVENTOR.

4E f; A i, l M, mw

Patented July 19, 1938 SIGNALIN G SYSTEM Free Calhoun, Chicago, Ill., assigner to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware 4Application February 17, 1937, serial No. 126,230

18 Claims.

'I'he present invention relates to signaling systems and more particularly to impulse repeaters for use in automatic telephone systems.

In conventional forms of automatic telephone 5 systems impulse repeaters of one type or another are employed in connection with inter-office trunk lines for the purpose of reducing to a minimum the number of conductors constituting the trunk line cables and for interrupting the circuits of such trunk lines in accordance with electrical impulses produced by operation oi impulsing means or a dialing device embodied in any substation connected to any calling subscribers line. The impulses as thus repeated comprise rapid fluctuations in the. current through the trunk line conductors, the impulsing rate being determined by the dial speed of the impulsing means, and these current impulses cause the operation of control means, usually in the form of line relays for selector or connector switches associated with the trunk lines.

Recent improvements in the design of line relays have given rise to the problem of improving the repeater circuits generally. 'I'hese line relay improvements, designed primarily to increase the sensitivity thereof to received electrical impulses, have rendered unsatisfactory those forms of repeater circuits such, for example, asthe high impedance bridge type, wherein the repeater relay is, during the operation of the repeater, subjected to transient impulses which tend to produce false operation of the repeater relay. One

, form of repeater circuit which is well adapted to meet the requirements of highly sensitive line relays is'the well-known repeating coil type. The circuit of this type of repeater includes primary repeating coils connected in series with the incoming line conductors and terminating at a repeater line relay, the line relay being shunted by a capacitor for by-passing voice frequency currents. These primary repeating coils are inductively coupled to secondary repeating coils connected in series with the conductors of the trunk line terminating at a distant selector or connector switch, the circuit of the lattertrunk line being interrupted in accordance with the transmitted impulses by .means of the repeater line relay.

The satisfactory operation of any impulsing' ar-- rangement vand more particularly an arrangement of the type briefly described above is measured by the ability of the device or control means to be controlled by .the transmitted impulses faithfully to follow the impulses created at the impulsing device and repeated over the interconnecting trunk lines by the impulse repeaters. If any substantial amount of distortion is introduced in the impulses in the transmission path between the impulsing device and the control means faithful response of the latter means can- 5 not be obtained. Such distortion may take any one of a variety of forms. Thus, if the period of energization of the control device is greatly less than the contact make period of the impulsing means, the device may have insuiicient time 10 in which fully to operate. Conversely, if the period of -de-energization of the control device is substantially less than the contact break period of the impulsing means, the device may have insuicient time in which to de-energize and pre- 15 pare for a succeeding impulsing cycle. Again, if any one of the vline relays in a chain of repeaters is falsely operated more than once during any one impulsing cycle of the impulsing means, false operation of the control device may result. 20

In a system of the type indicated, the amount of impulse distortion is determined at least in part by the relationbetween the circuit constants of the line to which the dialing-or impulsing de- 'Vice is connected, the constants of the elements 25 of the repeater associated with the line, the constants of any other apparatus associated with the line as, for example, normally inactive bridged ringers on =a party line, the rate of impulsing at the impulsing means, and to alesser extent by 3Q the voltage of the operating batteries and the line constants of succeeding trunk lines and the constantsof the impedance elements associated therewith. Usually the circuit constants of the individual subscribers lines and the trunk lines 35 are .xed by the physical arrangement of the system and cannot economically4 be altered. The impulsing rate may have any value within a range, the range usually extending between 8 and 12 interruptions per'second. It will be appreci- 40 ated, therefore, that the impulsing characteristics of the subscribers lines associated with a particular group of repeaters will vary over a wide range and when the impulsing conditions inherent in a particular subscribers line are particu- 45 .larly unfavorable, the impulse distortion obtained may, even with a repeater circuit of the type specified, be so great as to preclude faithful operation of the control device to be controlled by the transmitted impulses. More specifically, a 50 subscribers line may be in a condition which is perfectly satisfactory' for efdcient transmission of voice currents and yet be in a condition which is extremely unfavorable to impulse transmission thereover. 'I'his usually occurs in cases where 55 the subscribers line circuit is excessively long so that the line resistance thereof is high, or where the shunt leakage resistance between the line conductors-is extremely low, or by a combination of these two factors.

Under the conditions stated. the forrn of distortion which occursis manifested in a false energization and de-encrgization of the line relay included in the iirst repeater of the repeater chain, causing a.false operation of this relay which is repeated through the chain of relays to the control device. As will be pointed out in detail hereinafter, the reason for such false energization is that the circuit constants of the calling subscribers line, the elements of the nr repeater, and any other apparatus associated with the calling subscribers line are necessarily so related to each other and to the impulsing rate as incidentally to cause, in each impulse cycle, a voltage transient across the windings of the rst repeater line relay during the period of the cycle when this relay is supposed to be interrupted and corresponding to the interrupted period of the calling subscribers line circuit.,r

It is an object of the present invention, therefore, to provide in a system of the character described an improved repeater capable of operating in conjunction with any subscribers line circuit having reasonable voice frequency transmission efficiency in a manner such that impulses transmitted over the line may successively be repeated with tolerable distortion.

It is a further object of the invention to provide in a signaling system an impulse repeater arrangement, comprising a plurality of tandem connected repeaters, which is capable of producing faithful response of the impulse controlled means in accordance with impulses transmitted by impulsing means through the repeaters, and in which at least one of the repeaters is adapted to be connected to any one of a number of subscribers lines having a wide variety of impulsing characteristics.

More particularly, it is an object of the invention to provide an improved repeater of. the general type described which is capable of repeating substantially without distortion impulses received over a line having highly unfavorable impulsing characteristics.

In brief, the objects as set forth above are realized in accordance with the present invention by associating with at least one of the repeaters included in the repeater chain, reactance means for altering the circuit constants of the network between the impulsing device and the control means, thereby to reduce the impulse distortion in the impulse transmission path of the network to a tolerable value. More specifically, capacitance means isincluded in the first repeater of the repeater chain, in shunt with the voice frequency current by-passing capacitor and so proportioned relative to the circuit constants of a line having unfavorable impulsing characteristics. the elements of the associated repeater, and any other apparatus associated therewith that the electrical transient which occurs in each impulse cycle is delayed, following the interruption of the circuit of the line over which the impulses are transmitted, and the duration of the transient is increased. As a result, and for any reasonable impulsing rate, the circuit of this line is closed, during any one impulsing cycle,`before the expiration of the transient of the preceding impulsing cycle. In other words, each open circuit impulse perlod is ended in the normal manner by closing the line circuit to energize the first repeater, before the transient of the impulse has expired. Hence, the repeater line relay is not permitted to restore at the expiration of the transient and double operation of. the repeater relay during any single impulsing cycle is prevented. If desired, the delay may be achieved entirely through the action of the capacitance means shunting the voice-frequency by-pass capacitor of the first repeater. As an alternative, this capacitance means may be so proportioned that only a portion of the required delay is achieved thereby, an additional delay being obtained due to the operating inertia of the relays included in the repeater following the first repeater, such that the combined delay intervals for each impulse cycle extend well into eachsucceeding cycle. It is pointed out that the term repeater as used herein is a generic designation intended to connote anydevice or combination of devices for repeating impulses received over one line to 'a second line or to a controlled impulse responsive device directly.

The novel features believed to be characteristic of the invention are set forth withparticularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figure 1 illustrates in partially schematic form an automatic telephone system constructed and arranged in accordance with the present invention; Fig. 2 illustrates a portion of the system of Fig. 1 reduced to its simplest form; and Figs. 3 to 5, inclusive, are graphs illustrating the operating characteristics of typical installations.

Referring now more particularly to Figure 1 of the drawings, there is illustrated in partially schematic form a telephone system of the automatic type comprising a plurality of ofllces or exchanges ladapted to be inter-connected by trunk lines individually having associated therewith an impulse repeater for the purpose briefly described above. The system comprises four oilices or exchanges indicated at I0, Il, I2, and I3, respectively, with trunk lines extending between the oflices'in the conventional manner so that any subscribers line terminating at one oilice may selectively be connected to any other subscribers line terminating at the same or at any of the other omces by means of the usual line, selector and connector switches. This arrangement of elements for a connection between a subscribers line Il, comprising conductors Ii and I6, terminating at the ofce I, and a subscribers line terminating at the bank contacts of the connector switch included in the oilice I3 may comprise, connected in tandem, in the order named, a line switch I1, an intra-office threeconductor cable I8 including conductors I 9, 2II and 2l, a first selector switch 22, an impulse repeater indicated generally at 23, a two-conductor inter-oice trunk cable 24 comprising conductors 25 and 26, a second selector switch 21, a second impulse repeater 28, a second two-conductor inter-office trunk cable 29 comprising the conductors 30 and 3|, a third selector switch 32, a third repeater 33, a. third inter-office two-conductor trunk cable 3l comprising conductors 35 and 36 and, nally, a. connector switch indicated generally at 31. It will be understood that the enumerated selectorswitches, trunk lines, repeaters and the connector switch individually represent a number of similar elements located in and inter-connecting the various ofces. The line, selector and connector switches may be of any desired type, although preferably the line switch is of the rotary type and the selector and connector switches are of the well-known Strow ger type embodying a contact selector element adapted to be translated vertically and then -rotated in response to the selective and repeated operation of vertical and rotary control magnets, respectively. Sin'ce these switches are entirely conventional in form, they have been indicated only schematically in the drawings.

The line 4 is shown as being of the party line type having a plurality of subscribers substations connected thereto, one of -which is shown in detail at 39 and another of which is shown` schematically at 40. Each of these substations is of the well-known booster type embodying selective harmonic ringers. Thus, the station 39 comprises a ringer circuit including a ringer 4| and a condenser 42 connected in series across the line |4. This circuitis connected in shunt with a winding 43 of the booster transformer through the upper contact 44 of a hook switch 45, a

transmitter 46, contacts 41 and 48 of impulsing means-in the form of .a dialing device 49, and the lower contact 59 of the hook switch 45. A receiver 5| is provided which is connected between one terminal of the transmitter 46 and the junction point between the ringer 4| and the condenser 42 through the second winding 52 of the booster transformer. Gif-normal springs indicated at 53 are also provided which are adapted to short circuit the transmitter 46 and receiver 5| during the transmission of impulses. It is pointed out here that the words impulsing cycle .as used herein denote the cycle of opening the contacts 41 and 48 for a predetermined period determined by the rate of impulsing to interrupt the circuit of the subscribers line I4, and the closing of these contacts for a predetermined period, also determined by the rate of impulsing, thereby to close the circuit of the line I4.

The control means or device which, in the system shown, is to be controlled by the impulses transmitted by the impulslng means 49 comprises the connector switch 31 and, more par.- ticularly, a line relay 53 which is connected to the trunk conductors 35 and 36 when this particular connector switch is seized. The relay 53, as is well known, controls, through a system of interconnected relays, the operation of the vertical and rotary stepping magnets of the connector to cause the selector element to select the proper set of bank contacts leading to the called subscribers line. Since the manner of connecting such relays and their mode of operation is well known,. they have been omitted from the system in order to simplify the drawings.

Each of the repeaters 23, 21 and 33 included in the transmission path between the subscribers line |4 and the connector switch 31 is preferably of the well-known repeating coil type with the exception of the repeater 23 which is modified by the addition of means for reducing to a tolerable value distortion of the impulses in the manner described in detail hereinafter. For this reason, the repeater 23 only, has been shown in detail. It comprises the usual repeating coil transformer 56, including primary windings 51 and 58 and secondary windings 59 and 60 serially connected, respectively, in the cable conductors extending from the selector switch 22 and the cable con ductors 25 and 26 comprising the trunk line 24.

The windings 51 and 58 are connected in series with the windings of a repeater line relay 10 through the contacts 3| and 82 of a battery reversing shunt relay 80. A capacitor 63 is provided in shunt with the windings of the relay 10 for by-passing voice-frequency currents -around these windings and additional capacitance'means comprising the capacitor 64 shunting the windings of the relay 10 ls also provided for reducing impulse distortion to a tolerable value in the manner to be described in detail hereinafter. Also shunting the upper winding of the relay 10, during the circuit interruption period of each impulse cycle, is 4a priming resistor 65 which functions partially to energize the relay 10 and to render it more sensitive to received impulses. In order to repeat these impulses over the trunk line 24 the relay 10 is provided with a front armature 1| and associated contact 12 which are inserted in the conductor 25. The relay 10 is also provided with an armature 13 and associated contacts 14 and 15 for controlling a slow-to-release relay 90 and for removing the resistor 65 from in shunt with the windings of the relay 10 during the closed circuit period of each impulse cycle. One of the windings of the shunt relay is connected in' series with the secondary windings 69 across the trunk line conductors 25 and 26 and is shunted by a voice-frequency bypass condenser 66. The other winding of the;

relay 80 is adapted to be energized from the common battery at the contact 9| of the slow-torelease relay 90, so that when the called subscriber lifts his receiver the relay becomes fully energized to operate its battery reversing armatures and contacts 8346, inclusive in the usual manner.

The slow-to-release relay 99 is also provided with contacts 92 and 93 and an armature 94 for removing negative battery from the guarding conductor I9' when the relay is operated and for substituting guarding ground. An additional armature 95 and associated contact 95 are included in this relay which are connected in the circuit of the resistor 65.

Neglecting for the -present the additional capacitance means 64 and -its function, the system as generally described above is entirely conventional in form and its operation is well understood in the art. scribers substation 39 to a subscribers line terminating in the bank contacts of the connector switch 31 is initiated by lifting the receiver at the substation 39 to operate the hook switch 45 and close the contacts at 44 and 50, thereby causing the line switch |1 to select in the usual manner an idle rst selector switch, as, for example, the rst selectorl switch 22. This operation also places ground on the control conductor I9 in the usual manner, which ground extends over this.

conductor by way oi' the line switch contacts to the associated connector bank contact to busy the line |4 and thereby prevent its being seized due to an incoming call thereto. In response to successive operations of the impulsing means or dialing device, the selector switches 22, 21 and 32 are successively operated in the usual manner individually and successively to select idle trunks as, for example, the trunk lines 24, 29, and 34, extending between the oillces 2, 3, andf4. During these dialing operations, contacts 41 and 49 are periodically opened and closed to send electrical impulses over the line |4, which impulses are repeated over the trunk circuits by the repeaters 23, 29 and 33. Thus, at the conclusion In brief, a call from the subthat the restoration of the apparatus shown,

of the operation of the first selector 22 to select the idle trunli: I8 in response to the dialing of the nrst digit, the contacts 41 and 48 are closed to energize the repeater line relay 10 over an obvious circuitand thereby to condition the repeater 23 to repeat the impulses of the second digit to the second selector switch 21. The operation of the relay 10 causes the operation of the slow-to-release relay 80 over the circuit extending from ground at the armature 18, the contact 14, the winding of relay 80 to battery, and also closes the circuit of the trunk line 24 at the contact 12. When the slow-to-release relay 80 operates, it places guarding ground on the conductor I8' at contact 82, completes the circuit for partially energizing the relay 80 at contact 8| and prepares the circuit for the shunt priming resistor 85 at contact 88. The circuit of the priming resistor 65 is held open during the periods when the contacts 41 and 48 are closed by the relay 10 at back contact 15. It is pointed out that the windings of shunt relay 80 are so poled relative to each other that during the calling operation the fluxes thereof are additive and the relay remains de-energized. However, when a call is completed and the called party lifts his receiver, the current through the winding in series with the repeater coils 58 and 80 is reversed, causing the relay to operate, thereby to reverse the polarity of potential applied to conductors I5 and i8 at the armatures 84 and 86. At this stage of the operation and when the contacts 41 are opened for the nrst time during the dialing of the second digit, the line relay 10 is deenergized to open at contact 1| the circuit of the trunk line 24 and to open the circuit for the slow-to-release relay 80 at contact 14. The latter relay', however, being s'iow to release, stays operated until the relay 10 is again operated during the next impulse cycle. Further impulse cycles produced at the contactsof the dialing device cause alternate operation and restoration of the line relay 10, thereby repeating these impulses over the circuit of the trunk line 24 at the contact 12. Following the operation of the selector switches and the connector to select the called subscribers line, the usual operations of applying ringing potential to the called subscribers line, guarding the called line against seizure, and the like, are carried out in the conventional manner by means of apparatus, not shown, and forming no part of the invention. Since the systemas thus far described is entirely conventional it is beliefeld lowing the termination of a call, will be apparent to those skilled in the art and for that reason a description thereof is unnecessary.

Referring now more particularly to Fig. 2 of the drawings, there is illustrated the circuit of Fig. l in diagrammatic form, with the circuitimpedances of the subscribers line I4 and the associated impedance elements shown in detail. Thus, the series resistance of the line is represented by the resistors |00 and |0|; the shunt leakage resistance between the conductors I5 and I8 is indicated by the dotted line resistor |02; the capacitance between the line conductors I5 and I8 is shown by the dotted line capacitor |08; the impedance of series with the contacts of the impulsing device is indicated by the inductor |04; the impedances of all the ringer circuits of the line are indicated by the serially connected condenser |08 and induetor |05, and the windings of the line repeater relay 10 are indicated at |01 and |08, respecthe elements of substation 89 in tively.. Other elements of the circuit are identifled by the same reference characters as are used in the circuit of Fig. 1.

As was pointed out above, the faithfulness with which the line relay 10 responds to impulses received over the line |4 and occasioned by the operation of the impulsing device including the contacts 41 and 48, depends upon therelation between the rate of impulsing, the circuit constants of the line, and the impedance elements associated therewith. Thus, with a normal impulsing rate within the range of from 8 to 12 interruptions per second and an extremely long line wherein the values of the resistors |00 and |0| are high, the current through the relay windings |01 and |08 may be insumcient to cause the relay 10 to operate. This problem is obviated by the use of the relay priming resistor 05 as noted above which effectively shunts, during the open circuit period of each impulse cycle when the relay 10 is restored, a sui'llcient amount of current from around the loop circuit so that when the contacts 41 and 48 are closed, the added current through the windings |01 and |08 causes positive operation of the relay.

It was further pointed out above that one form of impulse distortion which occurs in the impulse transmission path is caused by the voltage transient which occurs following the opening of the contacts of the impulsing device 48 at the end of the closed contact period of eachl impulse cycle. 'I'his transient is caused by the rapid demagnctization oi' the relay 10 and functions to raise the line voltage between the conductors I5 and I8 to a value which may be several times the normal line voltage. The polarity of this voltage transient is opposite' that of the station battery' but so greatly predominates thereover, that the capacitors |08, |08, and 88, shunting the line are charged to a high potential. It is pointed out that the distributed capacitance |03 of the line is of such a value as to have practically no eect on the magnitude or duration of the transient. The voltage transient in each impulse cycle reaches its peak at about the instant the relay 10 restores. Following the charging interval, the capacitors |08, |08, and 88 discharge through the relay windings I01 and |08 and cause the relay to re-operate. Such spurious or false re-operation of the relay is somewhat momentary but if the series resistance |00, |0I is high, corresponding to a long line, the duration of the transient may be sufficient to cause re-operation of the distant control means which, in this case, comprises the line relay 58 of the connector switch I8. Such re-operation of the relay 58 may result in the controlled vertical or rotary magnets taking two steps in each impulse cycle.

The above described phenomenon is, among other factors, dependent upon the value of the shunt resistance of the line |4 including the leakage resistance |02 across the conductors In and |8 of the line circuit |4, and also upon the value of the combined capacitance of the l:apacltors 68 and 84. Thus, with the resistor i' chosen to provide the greatest sensitivity of the relay 10 or of a value of approximately 2,000 ohms, a shunt leakage resistance of the order of 10,000 ohms to infinity, and the usual value of two microfarads for the voice-frequency by-pass capacitors 88 there is insufllcient damping of the transient, with the result that the voltage transient as above descri d occurs and is of suillcient duration to c false operation followed by a restoration of e line relay 18. The magnitude of this transient also depends upon the voltage of the common battery in the oiiice I0 since the voltage across the windings of the relay 10 determines the rate of demagnetization thereof. Thus, if, in a given case, the voltage is reduced from 56 to 52 volts, false operation of the relay 10 may be entirely eliminated. With a 4low shunt leakage re-v sistance between the line conductors, of the order of 5,000 to 10,000 ohms, the transient which occurs is sufliciently damped so that false operation of the relay 10 due to the cause described above is eliminated. Under these conditions, however, aseconi'and equally undesirable transient results in each impulse cycle. This latter transient is caused by the opening of the circuitof the trunk line 24 at contact 12 when the line relay 10 restores in the usual manner. As this trunk circuit is opened, a current transient occurs in the secondary coils of the repeater transformer 56 which causes a voltage transient across the primary windings 51 and 58 of this transformer.

'I'his voltage transient aids the potential supplied v by the battery through the priming resistor 65 to the winding |01 in the sense that it flows through the shunt leakage resistance |02 in series with the line resistance |00, |0|, and thereby increasing the current through the windings |01 and |08 of relay 10. 'I'his added current causes a false reoperation of the line relay 10 which is repeated over the trunk conductors of the line 24. It is pointed out that, if the leakage resistance of the line is high, this second effect is prevented due to the discharging of the capacitors at about the time the transient caused by the opening of the trunk circuit occurs, since the polarities ofthe two transients are opposite. lUnder these conditions, however, the transient caused by the capac-y itor discharge is so greatly predominant that the transient produced by opening of the trunk circuit does not prevent the above described false operation of the line relay 10.

'Ihe exact nature of the impulse distortion which occurs is well illustrated in the graph of Fig. 3 which is an oscillographic record of the operation of a typical installation. 'Ihis graph was taken on a system embodying a single repeater and having the following circuit constants for the elements of Fig. 2:

In this graph, the line A represents the current through the winding |08 of the line relay 10, the line B represents the current in the circuit of the trunk line 24, and the line C indicates the opened and closed periods of the back contacts of the line relay associated with the second selector switch 21. When this last-mentioned line relay is deenergized these back contacts are c-losed and vice versa. In the line A, the points D and E denote respectively the instant when the 'circuit of the subscribers line |4 is interrupted at the contacts 41 and 48 and the instant when this line circuit is completed by these contacts during an impulsing operaticn and the distance D-D or E-E represents one `complete impulsing cycle.

`tion of the relay 10 occurs.

Points F and G or vune B indicate the instan at which the current impulses in the circuit o f the trunk line 24 produced by false operation4 of the relay 10 begin and end. andthe distance between these lines indicates the duration of the transient causing such false operation. The points H and Il indicate respectively the instants when the distant line relay of the second-selector switchl closes and opens its back contacts. It will be observed that, during each impulse cycle and shortly after the contacts at 41 open at the lnstants D, a current surge F-G occurs in the circuit of the trunk line 24 which causes a spurious or false operation of the distant relay at the second selector switch. Such false operation is probably the result of the transient caused by capacitor discharge, although the graph does not distinguish between the two causes'as described above. As will be noted from the first impulse I-H of the line C, this false operation takes the form of a complete energization and re-operation ofthe relay 10 followed by a complete restoring thereof. It is to be noted further that such false operations occur during each of the impulsing cycles. In the particular graph oi' this figure the false operation is of suiiicent dura.- tion to cause the control device, which may comprise the vertical or rotary magnets of the selector switch, to take a false step in the manner pointed out above, thus resulting in improper trunk line selection.

As previously pointed out, the rate of impulsing is another factor which partially determines whether or not distortion in the form of false operation of the first repeater line relay will occur. This is strikinglyemphasized by the graph of Fig. 4 which shows the operating characteristics of a system having the same characteristics as those for Fig. 3 with the exception that the combined capacitances of capacitors 63 and 64 were in this case 8 microfarads as contrasted with 6 microfarads for the system having the operating characteristics shown in Fig. 3. The same reference characters are used in Fig. 4 as in Fig. 3 to identify the same curves and the various points thereon. From Fig. 4 it will be observed that during the first impulse cycle and with an impulsing rate of exactly 8 interruptions per second no false operation of the relay 10 occurs. However, by the beginning of thev second impulse cycle the impulsing rate had decreased to 7.7 I. P. S. with the result that a false opera- During the third impulse cycle the impulsing rate was still less with the result that the false operation of relay 10 was still more pronounced. From this graph it is apparent that, for a given set of system characteristics, the impulsing rate cannot be decreased below a predetermined value without causing the form of impulse distortion noted.

In accordance with the present invention, the distortion as described above, namely, spurious or false operation of the relay 10, is prevented or reduced to a tolerable value by including in the repeater 23 reactance means comprising the additional capacitance means 64 for delaying, during each impulse cycle, the occurrence of the transient for an interval after the contacts at 41 and 48 have opened to interrupt the circuit of the subscribers line I4, and for increasing the duration of the transient sufliciently to permit the contacts at 41 and 48 to close and energize the relay 10 in the normal manner for the next impulse before the transient expires and the relay restores as a result of such expiration. This adbuilding up to a value sufilcient to cause operation of the relay, and the duration of the surge is increased to hold the relay operated for a greater time interval which overlaps the instant of reclosure of the contacts at 4l and 48, initiating the next impulse cycle. Thus, referring again to Iilg. 4, it will be seen that during the nrst half impulse cycle D-E, the transient as indicated by the current of the line 24 during the interval F-G overlaps the instant E when the contacts 41 and 48 are reclosed to initiate the next succeeding impulse cycle. Hence, when the transient is over and the relay 10 would normally tend to restore, it is held energized by virtue of the reclosure of its energizing circuit in the usual manner. It is pointed out here that the operating inertia of the relay 10 assists in increasing the operated time interval of the relay to make this interval overlap the reclosure instant E. In regard to the second impulse wherein the impulsing rate has decreased to '7.7 I. P. S. the transient occurs at the same instant in the impulse cycle as for the ilrst half cycle but the delay in the reclosure instant E of the second impulse cycle caused by the decrease in impulsing rate permits the transient F-G-to expire and the relay 10 to restore before the instant E arrives. Thus, false operation of the relay occurs during this and succeeding impulse cycles.

From the foregoing discussion with reference to Fig. 4, it will be apparent that for an impulsing rate above 8 interruptions per second and with the additional capacitance means 64 having a value of 8 microfarads, the latter element is so proportioned relative to the circuit constants of the line I4 and the constants of the other impedance elements associated with this line, including the elements of repeater 23, that the transient causing the false operation of the relay 10 holds the relay operated, during each impulse cycle, until the reclosure instant E occurs. It is pointed out that the circuit parameters given above for the system, upon which the operating characteristics of Fig. 4 are based, represent extremely unfavorable impulsing conditions and that any line having more favorable impulsing characteristics will operate perfectly satisfactorily in conjunction with the repeater as described above and having the present invention embodied therein. It is further pointed out that the shortening of the period representing the restored condition of the control means.. due to the false operation of the relay 10, is not sufllcient to have any adverse eiect on the operation of the control means. In other words, the ratio of the restored period of the control means to the energized period of the control means is well within the range which permits complete operation and restoration of this means during each impulsing cycle.

In the system as described above impulse distortion in the form of false operation of the rst repeater line relay is entirely eliminated by delaying, andvincreasing the duration of, the electrical transients causing false operation of the first impulse repeater line relay 10. If desired, andin those arrangements such as that illustrated wherein a number of repeaters are connected in tandem, at least a portion of the required delay may be supplied by the repeater line y peater Il'. Each relays of the repeaters following the nrst reof these relays has a certain operating and restoring inertia such that a time interval elapses between energization and operation and between de-energization and restoration. The total operating interval representing the sum ot the individual operating lags of the relays when added to the instant when false operation of the relay 1l occurs gives the instant when false energization of the distant control device occurs. Moreover, the interval corresponding to the combined restoring lags of these relays effects an increase in the interval during which the distant control means is falsely operated, thereby insuring that the false operation for each impulse cycle will continue weil into the succeeding cycle. It was found that such operating and restoring lags caused a change in the ratio of the open-circuit period to the closed-circuit period for each impulse received at the distant control device fromthe ratio of these intervals as originally transmitted at the impulsing device, but not to an extent sufficient to cause undesired operation of the device ultimately to be controlled. 'Ihis effect is well illustrated by the graph of Fig. 5 which is similar to those of Figs. 3 and 4 but shows the operating characteristics on a system including three repeaters connected in tandem over trunk lines. The characteristics of the system were as follows:

Operating voltage at all stations volts 42 Impulsing rate I. P. S 12 Subscribers vline series resistance ohms 0 Subscribers line leakage shunt resistance nhms 5,000 Series resistance of each trunk line ohms 250 Leakage shunt resistance of each trunk line nhmg 10, 000 Primings resistor in rst repeater ohms 2,000 Capacitance shunting line relay windings of rlrst repeater microfarads-- 8 Substations on Subscribers line 6 In the graph the line A represents the current through the negative winding of the first repeater line relay, the curve B' represents the current through the windings of the distant control device which in this case was the linerelay 53 of the connector switch Il, and the curve C' represents the open and closed contact periods of the control device. The distance D-E' indicates the open contact interval of the impulsing device 49 and the distance H'-I indicates the corresponding interval during which the distant control device is de-energized. Likewise the distance E'-D' is a measure of the closed contact period of the impulsing means and the distance I-H is a measure of the corresponding interval during which the control device is energized. This graph strikingly illustrates the effect of the inertia of the relays in delaying the response of the control device. Thus, during the iirst impulse cycle, operation of the control device occurs almost at the end of the rst half of the ilrst impulse of the impulsing means as shown by the distance, along the time axis, between D' and H'.

It will be understood that if the impulsing conditions of the trunk lines, as for example the lines 24 and 29, interconnecting the various repeaters are particularly unfavorable it may be necessary to employ additional capacitance means in each of the repeaters in the manner described above for preventing false operation of the control means atthe distant oilice or station. *In most instances, however, the trunk line characteristicsare more favorable to impulse transmission than the subscribers lines and consequently the expedient mentioned is unnecessary.

In practicing the invention as described above, the capacitor 63 and the additional capacitance means 64 may consist of two separate elements or they may be combined in the form of one capacitor having the appropriate capacitance value. In either case it has been found that if the total capacitance across the windings of the relay 10 is 8 microfarads,v satisfactory operation is obtained when the repeater is operated in a sys tem having the following characteristics:

Priming resistor 85 ohms-- 2,000 Series resistance of subscriber's lin 14...r -ohms-- `04,250 Shunt leakage resistance of line 14 ohms-infinite resistance-- 5,000 Series resistance of each trunk line ohms each 0-750 Shunt leakage resistance of each trunk line ohms-infinite resistance-- 10,000 Impulsing rate I. P. S-- l 8-12 Station battery voltage volts-- 42-56 Number of substations on line 14 1-6 Number of trunk lines in tandem with line 14 1-3 Number of repeaters in tandem 1 3 The above parameters and physical characteristics of the system shown are given by way of `example only since many other relationships between the various factors. involved may be used without departing from the invention herein disclosed.

While there has been described vwhat is at present considered to be the preferred embodiment of the invention it will be understood that various modifications may be made therein and it is aimed, therefore, to cover in the appended claims all such modifications as fall within the true spirit andscope of the invention. i 1

I claim:

1. -In a signaling system comprising a line, impulsing means on said line and a repeater adapted to be connected to said line to repeat electrical impulses received over said line to a second line and wherein the circuit constants of said line, the associated repeater and other apparatus associated with said line are necessarily so related as incidentally to produce false operation oi said repeater following the interruption of the circuit of said line during an impulse cycle, the method of operation which includes, delaying said false operation for a time interval after the interruptionof said line circuit, and starting the next impulse cycle by completing the circuit of said line before said interval expires.

2. In a signaling system comprising a line, impulsing means. on said line and a repeater adapted to be connected to saidline to repeat electrical impulses received over said line to a second line and wherein the circuit constants of said line, the associated repeater and other apparatus associated with said line are necessarily so related -as incidentally to produce an electrical transient which causes false operation of said repeater following the interruption of the circuit of said line during an impulsing cycle, the method of operation which includes delaying the occurrence of said electrical transient for a time interval after the interruption of said line circuit, increasing the duration of said transient,

and starting the next impulse cycle before said transient expires by completing the circuit of said line: l

3. In a signaling system comprising a line, impulsing means on said line and a repeater adapted to be connected to said line to repeat electrical impulses received over said line to additional repeaters adapted to be connected in with said first-named repeater over additional lines. and wherein the circuit constants of said line, the associated lrepeater and other apparatus associated with said line are necessarily so related as incidentally to produce false operation of said repeater following the interruption of the circuit o i' said .line during an impulse cycle, which false operation Ais repeated by the other repeaters of the system, the method of operation which comprises, delaying said false operation of said repeater for a time interval after the interruption of said line circuit, delaying in said additional repeaters and for a. further time interval the eil'ect of said false operation on the last of said repeaters, and starting the next impulse cycle before the combined timeintervals have expired.

4. In a signaling system comprising a line, impulsing means on said line and a repeater adapted to be connected to said line to repeat electrical impulses received over said line to additional repeaters adapted to be connected in tandem with said first-named repeater over additional lines, and wherein the circuit constants oi' said line, the associated repeaters and other apparatus associated with said line are necessarily so related as incidentally to produce electrical transients following the interruption of the circuit of said line during an impulsing cycle thereby to cause false operation of said first repeater, which false operation is repeated bythe other repeater or repeaters, the method of operation which comprises delaying the occurrence of said transient for a time interval after the interruption of said line circuit, increasing the duration of said transient, delaying insaid additional repeaters and for a further time interval.

- impulses, said repeater being operative to repeat said impulses over a second line, said first-named line, impulsing means and repeater necessarily having included therein and associated therewith impedances which tend to produce false impulsing of said repeater, and reactance means associated with said repeater and so proportioned relative to said impedances as to prevent said false impulsing.

6. In a signaling system, a line, impulsing means for alternately closing and interrupting the circuit of said line at a predetermined rate to transmit electrical impulses thereover, an impulse repeater adapted to be connected to said line and including a relay energized when the circuit of said line is closed and de-energized when the circuit of said line is interrupted, said relay operating to repeat said impulses over a second line, means necessarily included in and associated with said first-named line for incidentally producing false energization of said relay during the time interval of each impulsing cycle when the circuit of said line is interrupted, and reactance means associated with said relay for preventing, during each impulse cycle, thede-energization of said relay after its false energiaation.

7. In a signaling system, a line, impulsing means for valternately closing and interrupting the circuit of said line at a predetermined rate to transmit electrical impulses thereover, an impulse repeater adapted to be connected to said line and including a relay energized when the circuit of said line is closed and de-energized when the circuit of said line is interrupted, said relay operating to repeat said impulses over a second line, means necessarily included in and associated with said mst-named line for incidentally producing, during the period of each impulse cycle when the circuit of said line is interrupted, an electrical transient which causes false energlzation of said relay, and reactance means associated with said relay for delaying, during each impulsing cycle, the occurrence of said transient following the interruption of the circuit of said line and for increasing the duration of said transient, whereby the circuit of said line is closed during any one cycle before the expiration of the transient of the preceding cycle.

8. In a signaling system, a' line, impulsing means for alternately closing and interrupting the circuit of said line at a predetermined rate to transmit electrical impulses thereover, an impulse repeater adapted to be connected to said line and including a relay energized when the circuit of said line is closed and deenergized when the circuit of said line is interrupted, said repeater being operative to repeat said impulses over a second line, means necessarily included in and associated withl said iirst-named line for incidentally producing, during the period of each impulse cycle when the circuit of said line is interrupted, an electrical transient which causes false energization of said relay, a resistor adapted to shunt the winding of said relay to increase the sensitivity thereof to received impulses and incidentally to increase the sensitivity of said relay to said transient, and capacitance means shunting said resistor for delaying, in each impulse cycle. the occurrence of the transient i'ollowing the interruption of the circuit of said line and for increasingv the duration of said transient, whereby the circuit of said line is closed during any one impulsing cycle before the expiration or the transient of the preceding impulsing cycle.

9. In a telephone system, a line, impulsing means on said line for transmitting electrical impulses thereover, an impulse repeater adapted to be connected to said line and including repeater windings for transmitting voice frequency currents over a second line, a relay included in said repeater having windings connected in series with a portion of said repeater windings, said relay being operative to repeat said impulses over said second line, the circuit constants of said firstnamed line, the elements of said repeater, and any other apparatus associated with said nrstnamed line necessarily being so proportioned as incidentally to cause intolerable distortion of the repeated impulses, and capacitance means shunting the windings of said relay and so proportioned relative to said circuit constants that said distortion is reduced to a tolerable value.

l0. In a telephone system, a line, impulsing means on said line for transmitting electrical impulses thereover, an impulse repeater adapted to be connected to said line and including windings for transmitting voice frequency currents over a second line, a relay included 1n said repeater having windings connected in series with a portion of said repeater windings, said relay being operative to Irepeat said impulses over said second line, resistance means adapted to shunt the windings of said relay, the circuit constants of said first-named line, the elements of said repeater including said resistance means, and any other apparatus associated with said first-named line necessarily being so proportioned as incidentally to cause intolerable distortion oi the repeated impulses, and capacitance means shunting the windings of said relay and so proportioned relative to said circuit constants that said distortion is reduced to a tolerable value.

11. In a telephone system, a line, impulsing means on said line for transmitting electrical impulses thereover, an impulse repeater adapted to be connected to said line and including repeater windings for transmitting voice frequency currents over a second line, a relay included in said repeater having windings connected in series with a portion of said repeater windings, said relay being operative to repeat said impulses over said second line, the circuit' constants of said first-named line, the elements of said repeater, and any other apparatus associated with said first-named line necessarily being so proportioned as incidentally to cause false operation of said relay during each impulsing cycle, and capacitance means shunting the windings of said relay and so proportioned relative to said circuit constants that said false operation of said relay is prevented from causing false repeated impulses.

l2. In a telephone system, a line, impulsing means on said line for transmitting electrical impulses thereover, an impulse repeater adapted to be connected to said line and including windings for transmitting voice frequency currents over a second line, a relay included in said repeater having repeater windings connected in series with a portion of said repeater windings, said relay being operative to repeat said impulses over said second line, a resistor adapted to shunt the windings of said relay, the circuit constants of said first-named line, the elements of said repeater including said resistor, and any other apparatus associated with said first-named line necessarily being so proportioned as incidentally to cause false operation of said relay during each impulsing cycle, and capacitance means shunting the windings of said relay and so proportioned relative to said circuit constants that said false operation of said relay is prevented from causing false repeated impulses.

13. In a telephone system, a line, impulsing means on said line for alternately closing and interrupting the circuit of said line to transmit electrical impulses thereover, an impulse repeater adapted to be connected to said Iline and including repeater windings for transmitting voice frequency currents over a second line, a relay included in said repeater having a. winding connected in series with a portion of said re peater windings, said relay being energized when the circuit of said first-named line is closed and deenergized with the circuit of said first-named line is interrupted, and being operative to repeat said impulses over said second line, a resistor adapted to shunt the winding of said relayI the circuit constants of said first-named line, the elements of said repeater, and any apparatus associated with said first-named line being necessarily so proportioned as incidentally to cause M5 a voltage transient across said relay windings suflicient to cause false energization and operation of said relay during the period of each impulse cycle when the circuit of said line is interrupted, and capacitance means shunting said relay windings and so proportioned relative to said circuit constants that said voltage transient is delayed and the duration thereof is increased, whereby said relay is not de-energized following the expiration of said transient.

14. In a signaling system, a line, impulsing means for transmitting electrical impulses over said line at a predetermined rate, an impulse repeater adapted to be connected to said line and including a relay for repeating said impulses over a second 1ine,the circuit constants of said rstnamed line, the elements of said repeater and any apparatus associated with said rst-named line necessarily being so related to each other and to said predetermined rate of impulsing as incidentally to cause intolerable distortion of the -repeated impulses, and reactance means connected in circuit with the windings of said relay and so proportioned relative to said circuit constants and said predetermined rate of impulsing that said distortion is reduced to a tolerable value.

15. In a signaling system, a line, impulsing means for transmitting electrical impulses over said line at a predetermined rate, an impulse repeater adapted to be connected to said line and including a relay for repeating said impulses over a second line, the circuit constants of said firstnamed line, the elements of said repeater, and any other apparatus associated with said rstnamed line being so related to each other and to said predetermined impulsing rate as incidentally to cause intolerable distortion oi' the repeated impulses, and capacitance means connected in shunt with the windings of said relay and so proportioned relative to said circuit constants and said predetermined rate of impulsing that said distortion is reduced to a tolerable value.

16. In a signaling system, a line, impulsing means for transmitting electrical impulses over said line, control means adapted to be controlled by said impulses, a plurality of impulse repeaters `and at least one additional line adapted to be connected in tandem to inter-connect said line and said control means, the circuit constants of said line, said additional lines, the elements of said repeaters and any other apparatus associated therewith being necessarily so related to each other as incidentally to cause intolerable distortion of the impulses received at said control means, and an impedance element associated With at least one of said repeaters and so proportioned relative to said circuit constants that said distortion is reduced to a tolerable value.

17. In a signaling system, a line, impulsing means for transmitting electrical impulses over said line at a predetermined rate, control means adapted to be controlled by said impulses, a plurality of impulse repeaters and additional lines adapted to be connected in tandem to inter-connect said line and said control means, the circuit constants of said line, said additional lines, the elements of said repeaters and of any other apparatus associated therewith being necessarily so related to each other and to said impulsing rate as incidentally to tend to cause false operation of said control means, and means comprising reactance means included in 'at least one of said repeaters for preventing false operation of said control means.

18. In a signaling system, a line, impulsing .means for transmitting electrical impulses over said line, control means adapted to be controlled by said impulses, a plurality of impulse repeaters and additional lines adapted to be connected in tandem to inter-connect said line and said control means, each of said repeaters including a relay for alternately interrupting and closing the circuit o-f its associated line in response to said impulses, whereby said impulses are transmitted to said control means, the circuit constants of said line, the elements of said repeaters, said additional lines and other apparatus associated therewith necessarily being so related toeach other as incidentally to cause intolerable distortion of the impulses received at said control means, the operating time interval of each of said relays being eiective to reduce said distortion, and capacitance means included in at least one of said repeaters in shunt with the ywindings of the associated relay and so propor-l 

